diy-PCB questions...

[freebird1127]

Hey guys,

   I'm fairly new to creating PCBs at home, so I thought I'd ask a couple of questions...

1)  I'm using a ferric chloride etchant.  Is it okay to etch PCBs in a glass pyrex dish or a plastic dish of some sort?  

2)  When I rinse the etchant off of my PCBs, should i rinse it in the bathtub / bathroom sink, or are ferric chloride and ceramic not the best of friends?  

3)  What's the best way to dispose of used ferric chloride?

4)  Do i have to worry about my plumbing being "etched out" of my walls?   :shock:

Any other useful hints anyone can give me would be more than welcome!

Thanks!!!
Evan Haklar

[Mike Nichting]

Hi Evan,
yes you can use a pyrex bowl or plastic bowl. Whichever is best for you. I use a Pyrex bowl.

You can dump the Ferric chloride down the toilet but be care full not to get it on anything because it will stain everything~!!

You can wahs the PCB off in the sink or bathtub but just make sure you wash all of the etchant off of any surface that you don't want it on RIGHT AWAY~!!! It stains quickly and I haven't had any luck washing it oof of my hands or other things that I left it on.

Good luck bro,
Mike Nichting

[gez]

Before you dump it down the bog/whatever, neutralise it with washing soda.  Do it in a HIGH sided container/something with a lid on, as the reaction causes everything to froth up and spill all over the place if you're not careful!  Do it bit by bit, but DO do it - it's better for the environment.

[BillyJ]

I'm no expert but in my experience plastic and glass are a ok.
So far so good anyway. I think it mostly eats metals.
I don't know how diluted it needs to be to protect metal pipes and such but I have heard you could do some damage so dilute well if that is what you do.
Baking soda is an akaline and will help neutralize the acid.
Be careful as it will foam up and make a lot more messy stuff than you think it may. Icky orange messy foam from heck. be prepared for this or look out.
On the rare occasion I have let this stuff down a drain I follow it up with a bunch of baking soda.
I am not sure what the BEST way to dispose of it is.
I would like to know though...

[MartyB]

Try putting the PCB and etchant in sealable GLAD-type sandwich or snack bags, and immersing them in a container of hot water, then sloshing the whole thing while visually monitoring the etching progress.  This method allows me to use a minimal amount of etchant and dispose of it easily.  I only need 15-20cc of ferric chloride to do two or three small PCBs at a time.  Wear gloves!

[freebird1127]

Great Idea Marty!  All of you have been very helpful!  Thanks alot guys!
Ev

[Paul Perry (Frostwave)]

Ferric chloride stains "stainless" steel. Badly. Permanently. This includes some bathroom fittings..

[ErikMiller]

Ammonium persulphate is much easier to deal with: you can see through it, so you can more easily tell when your board is finished etching, it doesn't stain (it bleaches, but not as aggressively as Ferric Chloride eats and stains), and it's not as destructive to the plumbing.

I used to etch one-off boards professionally, and I used nothing but ammonium persulphate.

It comes in crystal form, so you can mix only as much as you need.

[freebird1127]

Ammonium Persulphate... sounds good.  Where do I pick some up?
Ev

[Craig V]

I don't know where to get any, but definately try that bag method.  It is so much easier to clean up, and you use a lot less etchant.

[Hal]

Baking soda is an akaline and will help neutralize the acid.

_is_ FeCl3 an acid?  I guess it could be one of those crazy ones, but don't most acids have hydrogen in them?  I think FeCl3 is a salt.

FeCl3 + 3Cu -> 3CuCl + 3Fe    ?

looking at this, I see no way adding a base could help ...

I gotta brush up on my chemistry

[Peter Snowberg]

Yep, it would need a free hydrogen to be an acid, but lack of hydrogen doesn't necessarily make it less reactive. When you add water to ferric chloride crystals you get FeCl3:6H20, but I'm at a loss after that. The FeCl3 sure likes to attach, that much I can see.

[Paul Perry (Frostwave)]

FeCl3 is a "lewis acid".

[Hal]

haha yea its okay...as long as it works, we don't need to know how...


I guess it could be an "anhydrous acid"... the Fe+ and Cl- would Ionize, and OH- would bond with Fe, leaving a higher hydrogen concentration...

Hmmm  I think I'm gunna ask my old chemestry teacher tomorow.

[amz-fx]

When you mix the ferric chloride granules with water, some hydrochloric acid is formed through hydrolysis:

FeCl3 + H20 -> Fe(OH)3 + 3HCl

This makes the solution acidic.  Once the copperclad board is added, some of the copper directly replaces the iron in the solutions because of the difference in electronegativity of the metals and you get a mixture of iron and copper hydroxides, some of which precipitate, and consequently, etching of the board.

regards, Jack

[ErikMiller]

You can get ammonium persulphate here:

http://www.mgchemicals.com/products/410.html

One warning: apparently it will wash off etch resist pen ink. Its cousin, sodium persulphate, will not.